A steam plant of this type conventionally includes one or more steam drum(s) with associated evaporators with which, in particular at different pressure levels, steam is generated which can be supplied to a steam turbine. Impurities in the water-steam circuit of the steam plant have to be removed. Concentration of the impurities takes place in the steam drum. Non-volatile substances remain in the steam drum owing to removal of wet steam from the steam drum. These non-volatile substances are removed from the circuit by blowing down. Waste water and steam also occur in the water-steam circuit, in particular during start-up and shutdown of the steam plant, as a result of removed water, which does not contain any impurities but is nevertheless largely discarded and not used further. In the process the circuit loses water which has to be re-supplied by make-up water, or what is known as deionized water. The replenished deionized water has high oxygen and carbon dioxide contents which require degassing of the deionized water, so the start-up time of the steam plant is extended. Costs also result and the environment is polluted.
It is known that with the steam drum of an individual pressure level the blown down water is relaxed in a separator tank and water and steam are separated from each other. The separated steam is subsequently conveyed at low pressure into a collecting tank for degassing and heating of water contained therein. The separated contaminated water is treated in a water treatment plant and subsequently supplied to the water-steam circuit. It is also known that water removed from steam conduits is supplied to the turbine condenser directly or via separator bottles.